Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic disease in this country. If affects 500,000 people and costs in excess of $200 million per year for treatment of ESRD alone. Thus, it is important to expand our understanding of this disease. Our large and well-studied ADPKD population includes 386 families, six of whom are know to be ADPKD2 (chromosome 4). 655 adults with ADPKD, 149 children with ADPKD, and 131 unaffected children (defined by ultra- sonography) have participated in the study since 1985. The project's specific aims reflect information gathered by us and others and utilize the recent cloning of the ADPKD1 and ADPKD2 genes. There are three specific aims. First, we will attempt to elucidate the relationship between phenotypic and genotypic variability by focusing on children with every early onset disease and the phenotypic differences between ADPKD1 and ADPKD2 children. The second aim is to further our understanding of ADPKD in children by identifying prognostic phenotypic characteristics in the children and in their parents. The third aim is to conduct a randomized, interventional study on the effect of intensive or standard antihypertensive therapy on the progression of renal structural disease in ADPKD children.